Current-voltage conversion circuit

Abstract

A current-voltage conversion circuit which converts a current to be detected into a voltage, includes a detection resistor, amplifier circuit having a first operational amplifier, and an offset adjusting current source having a third resistor and a fourth resistor which are capable of trimming. The offset adjusting current source causes an offset adjustment current to flow in the offset resistor. The current value of the offset adjustment current is controlled by adjusting the resistance of the third resistor and the fourth resistor. A voltage at a node between the first transistor and the second resistor is output.

1. A current-voltage conversion circuit which converts a current to be detected into a voltage, comprising:
 a detection resistor provided on a path through which the current to be detected flows; 
 a first resistor, a first transistor and a second resistor connected in series between a high-potential first terminal of the detection resistor and a first fixed voltage terminal; 
 a first operational amplifier which has its output terminal connected to the control terminal of the first transistor, and has its inverting input terminal connected to a node between the first resistor and the first transistor; 
 an offset resistor which is provided between a low-potential second terminal of the detection resistor and the non-inverting input terminal of the first operational amplifier; 
 an offset adjusting current source which includes a trimmable resistor and causes an offset adjustment current to flow in the offset resistor, the current value of the offset adjustment current being controlled by adjusting the resistance of the resistors, wherein 
 a voltage at a node between the first transistor and the second resistor is output. 
 
   
   
     2. The current-voltage conversion circuit according to  claim 1 , wherein
 the offset adjusting current source comprises: 
 a reference voltage circuit; 
 third and fourth resistors which divide a reference voltage output from the reference voltage circuit; 
 a second transistor and a fifth resistor connected in series between the non-inverting input terminal of the first operational amplifier and a second fixed voltage terminal; and 
 an operational amplifier which receives the reference voltage at the non-inverting input terminal, has its inverting input terminal connected to a node between the second transistor and the fifth resistor, and has its output terminal connected to the control terminal of the second transistor, wherein 
 at least one of the third resistor and the fourth resistor is trimmable. 
 
   
   
     3. The current-voltage conversion circuit according to  claim 1 , wherein the first resistor, the second resistor, the first operational amplifier, the offset resistor and the offset adjusting current source are integrated on a semiconductor substrate. 
   
   
     4. A power consumption detection circuit comprising:
 the current-voltage conversion circuit according to  claim 1 -which detects a current that flows in a load circuit; 
 an analog to digital converter which subjects an output voltage of the current-voltage conversion circuit to analog to digital conversion; and 
 a processing unit which determines power consumption of the load circuit by referring to the value of the output voltage subjected to analog to digital conversion by the analog to digital converter. 
 
   
   
     5. Electronic equipment comprising:
 a battery; 
 a load circuit driven by the battery; and 
 
     the power consumption detection circuit according to  claim 4  which detects power consumption of the load circuit, wherein the processing unit of the power consumption detection circuit determines the remaining capacity of the battery by referring to the power consumption of the load circuit.